JP6180976B2 - Ion accelerator, ion acceleration control method, and particle beam therapy system - Google Patents

Description

  Embodiments described herein relate generally to an ion accelerator that accelerates an ion beam generated using a laser, an ion beam acceleration control method, and a particle beam therapy system that performs treatment by irradiating an affected area of a patient with an accelerated ion beam. .

  2. Description of the Related Art Particle beam therapy apparatuses that perform treatment by irradiating an affected area (cancer) of a patient with an ion beam composed of carbon ions or the like are widely known.

  In this particle beam therapy system, ions extracted from an ion source are accelerated by a linear accelerator to generate an ion beam, and the ion beam that has been accelerated by a synchrotron (circular accelerator) and increased to the set energy is used for cancer treatment. Use.

  In an ion source that generates ions, a method is known in which ions are obtained by causing discharge in a gas using a microwave or an electron beam.

  In general, an ion source called an ECR (Electron Cyclotron Resonance) ion source (electron cyclotron resonance ion source) is used in an ion accelerator for cancer treatment. In this method, gas is ionized to generate plasma, and ions are extracted by an electric field.

  However, the ion beam generated from the ECR ion source is a direct current beam, and there is an upper limit on the maximum current value that can be extracted (usually several hundred μA). For this reason, the ion beam incidence to the synchrotron employs a multiple-time incidence method called multi-turn incidence to ensure the number of ions necessary for treatment.

  On the other hand, in recent years, the use of laser ion sources that generate an ion beam using a laser has become widespread. This laser ion source condenses and irradiates laser light onto a solid target, and vaporizes and ionizes the target element using the energy of the laser light to generate plasma. Then, ions contained in the plasma are transported as they are in the plasma, and are accelerated at the time of extraction (for example, refer to Patent Documents 1 and 2).

  In a conventional ECR ion source, an ion beam is drawn out in a direct current, but in a laser ion source, a pulse beam with a high peak (up to several μsec) is obtained. Although this laser beam is a short pulse (up to several μsec pulse width), a large current with a peak current of the order of mA can be extracted. Further, since ions are generated by a laser having high energy, multivalent ions can be generated.

  For this reason, since the number of ions required for cancer treatment or the like can be ensured by one pulse, it is possible to adopt a single-injection method called single-turn injection.

Japanese Patent No. 3713524 JP 2009-37764 A

  By the way, the ion beam incident on the synchrotron is accelerated into a circle called a bunch.

  When a pulsed high-current beam is incident on a synchrotron using a laser ion source, the current value circulating in the synchrotron is not uniform, and the rotation is accelerated in a time-distributed state. For this reason, when the number of bunches is 2 or more, there is a problem that a large deviation occurs in the current value of each bunch, and a large space charge effect is generated in a bunch having a high current value.

  This problem complicates the design and configuration of the instrument for stably accelerating the ion beam on the synchrotron.

  The present invention has been made in view of such circumstances, and provides an ion acceleration technique and a particle beam therapy apparatus that suppress variation in current value of each bunch when the ion beam is orbitally accelerated in a synchrotron. With the goal.

The ion accelerator of this embodiment includes a laser ion source that generates plasma using a laser, a linear accelerator that outputs an ion beam that is accelerated by extracting ions from the plasma, and the ion beam circulates in a circular orbit. And a high-frequency acceleration cavity for accelerating the ion beam that circulates on the circular orbit, and a synchrotron that makes the output ion beam incident and circulates and accelerates, without accelerating the ion beam A non-accelerated lap time setting unit for setting a time for circulating on the circular orbit of the synchrotron as a non-accelerated lap time, and the non-accelerated lap time has elapsed after the ion beam is incident on the synchrotron A synchrotron that activates the high-frequency acceleration cavity later to accelerate the ion beam It comprises a control unit, wherein the non-acceleration circulation time, the ion beam until circulating time difference due to the variation of energy with the ion beam incident becomes more circulation time of the ions having a nominal energy in the ion beam It is a time to go around without accelerating .

The ion acceleration control method of the present embodiment is provided with a deflection electromagnet for circulating an ion beam on a circular orbit and a high-frequency acceleration cavity for accelerating the ion beam circulating on the circular orbit, and makes the ion beam incident A step of generating plasma using a laser using a synchrotron that is circulated and accelerated, a step of outputting an ion beam accelerated by extracting ions from the plasma, and the synchrotron without accelerating the ion beam A step of setting a time for the tron to circulate on the circular orbit of the tron as a non-accelerated lap time; wherein the step of said orbiting accelerated ion beam, a Nde containing Te, the free acceleration circulation That while is the time to orbit without accelerating the ion beam to a higher circulation time of the ions having a nominal energy in circulation time difference due to the variation of energy with the ion beam incident said ion beam Features.

  ADVANTAGE OF THE INVENTION According to this invention, when accelerating an ion beam in a synchrotron, the ion acceleration technique and particle beam therapy apparatus which suppress the dispersion | variation in the electric current value for every bunch are provided.

The block diagram of the ion accelerator which concerns on this embodiment. The timing chart explaining control operation of the ion accelerator concerning this embodiment. (A) The figure which shows the time change of the electric current value of an incident ion beam, (B) The figure which shows the time change of the electric current value when an ion beam is made to circulate without accelerating with a synchrotron. (A) The figure which shows the time change of the electric current value of an incident ion beam, (B) The figure which shows the time change of an electric current value when an unaccelerated circulation time is set to 0.5 m (s), (C) An unaccelerated circulation The figure which shows the time change of the electric current value when time is set to 1 m (s). The flowchart which shows the acceleration control method of the ion beam which concerns on this embodiment. The lineblock diagram of the particle beam therapy system concerning this embodiment.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
As shown in FIG. 1, an ion accelerator 10 according to this embodiment includes a laser ion source 11 that generates plasma using a laser, a linear accelerator 12 that outputs an ion beam accelerated by extracting ions from the plasma, and an ion A deflecting electromagnet 17 for circulating the beam on the circular orbit and a high-frequency acceleration cavity 22 for accelerating the ion beam circulating on the circular orbit, and a synchrotron 16 for making the output ion beam incident to accelerate the circulation A non-accelerated orbiting time setting unit 28 for setting a time for the ion beam to circulate on the circular orbit without acceleration, and an unaccelerated orbiting time after the ion beam is incident on the synchrotron 16. After that, the synchrotron control unit 27 that activates the high-frequency acceleration cavity 22 to circulate and accelerate the ion beam, Obtain.
1 illustrates the configuration of the synchrotron 16, and the arrangement and quantity of each configuration are not limited to those in FIG.

  In the laser ion source 11, the solid target is focused and irradiated with laser light. Then, the element of the solid target is evaporated and ionized by the energy of the laser beam to generate plasma.

  The linear accelerator 12 is connected to the laser ion source 11 and introduces plasma generated from the laser ion source 11 to extract ions. Then, an ion beam obtained by accelerating the extracted ions is output. The output ion beam is increased to a predetermined energy using the drift tube linear accelerator 13.

  The incident beam transport system 15 is provided with a deflection electromagnet 14 for changing the trajectory of the ion beam on the transport trajectory, and transports the ion beam output from the drift tube linear accelerator 13 to the synchrotron 16.

  The synchrotron 16 is a circular accelerator for accelerating the ion beam incident from the incident beam transport system 15 to the required energy by circular acceleration.

  The synchrotron 16 is arranged in a circular shape, deflected electromagnets 17 for deflecting an incident ion beam to circulate on a circular orbit, and a high-frequency acceleration cavity 22 for accelerating the ion beam orbiting on the circular orbit. Is provided.

  In the synchrotron 16, an incident electrostatic septum 20 is disposed in the vicinity of the ion beam incident position, and an incident kicker electromagnet 21 is disposed at a position where the incident ion beam intersects the orbit. The incident electrostatic septum 20 and the incident kicker electromagnet 21 are activated (excited) when the ion beam is incident, so that the ion beam incident on the synchrotron 16 from the incident beam transport system 15 is placed on the orbit. .

  Further, the synchrotron 16 is provided with a quadrupole electromagnet 18 for controlling the convergence of the ion beam, a hexapole electromagnet 19 for correcting chromaticity (chromatic aberration), and the like to assist the circulation of the ion beam.

  The ion beam accelerated to the required energy is taken out from the outgoing beam transport system 23 using an outgoing bump electromagnet and a septum (not shown). Then, it is transported to an irradiation device installed outside the synchrotron 16 via the outgoing beam transport system 23 and used for cancer treatment or the like.

  The control device 24 controls a series of operations from the output of the ion beam, the circular acceleration in the synchrotron 16 to the extraction of the ion beam in synchronization.

  The control device 24 starts laser irradiation with the laser ion source 11, and controls the beam output from the linear accelerator 12, and the incident timing to the synchrotron 16 based on the output information of the ion beam. The timing control unit 26 that transmits to the synchrotron control unit 27, the synchrotron control unit 27 that controls the circular acceleration and extraction of the ion beam in the synchrotron 16, and the synchrotron 16 without accelerating the ion beam A non-accelerated lap time setting unit 28 that sets a lap time as a non-accelerated lap time.

The control operation of the ion accelerator 10 will be specifically described with reference to the timing chart of FIG. 2 (see FIG. 1 as appropriate).
The incident beam control unit 25 starts laser irradiation with the laser ion source 11 and outputs a short pulse ion beam from the linear accelerator 12.

  The synchrotron control unit 27 receives the timing of ion beam incidence from the timing control unit 26 and excites the incident kicker magnet 21 to place the ion beam on the orbit.

  The synchrotron control unit 27 does not start the high-frequency acceleration cavity 22 until the non-accelerated circulation time elapses from the timing of ion beam incidence, that is, the ion beam is orbited without acceleration.

  Then, after the non-acceleration circulation time has elapsed, the high-frequency acceleration cavity 22 is activated (excited) to accelerate the ion beam.

  The synchrotron control unit 27 maintains the acceleration state with the synchrotron 16 and executes extraction of the beam from the outgoing beam transport system 23 when the ion beam reaches the set energy. Then, the unnecessary ion beam is decelerated and removed, and a new ion beam is output.

  The ion beam from the laser ion source 11 is a short pulse high current beam. For this reason, the incident on the synchrotron 16 enables a single turn incidence in which a pulsed ion beam is incident in a single shot for one control operation.

  In the case of multi-turn incidence in which the beam is incident on the synchrotron 16 a plurality of times, the ion beam trajectory is shifted by installing an incident bump electromagnet on the circular orbit so that each ion beam does not enter the same orbit. There is a need.

  In this way, by making the ion beam incident on the synchrotron 16 as a single-turn incident, it is possible to reduce equipment necessary for the multi-turn incident such as an incident bump electromagnet.

  Next, the effect of providing a non-accelerated circulation time for circulating the ion beam without accelerating it will be described.

  FIG. 3 is a diagram showing a change in the distribution of current values in the ion beam when the ion beam is circulated without acceleration. FIG. 3A shows the time change of the current value of the incident ion beam, and FIG. 3B shows the time change of the current value after the ion beam is circulated without being accelerated by the synchrotron 16. Yes.

Here, a case where the pulse width of the beam incident on the synchrotron 16 is shorter than the circulation time t _{0 of} ions having the rated energy E ₀ in the ion beam will be considered.

  The definition of the beam pulse width may be, for example, twice the half width of the pulse (Full Width Half Mean: FWHM), 2σ of the standard deviation, and the width of a pulse including 90% of the particles constituting the ion beam. .

The incident ion beam is allowed to vary by E ₀ ± ΔE with respect to the rated energy E ₀ . This energy variation causes a difference in circulation speed, and the circulation time has a variation of t ₀ ± Δt. That is, there is a 2Δt orbital time difference in the incident ion beam.

  As the ion beam repeats the circulation of the synchrotron 16 and the circulation distance increases, the circulation time difference, which was 2Δt in the first circulation, increases as the circulation is repeated. As the circulation time difference increases, the peak value of the ion beam current value decreases and the ion beam is flattened.

Then, when the lap time difference caused by the energy variation of the incident ion beam becomes equal to the lap time t _{0 of the} ion having the rated energy E ₀ , that is, when the ion beam circulates t ₀ / (2Δt), ion beam will be uniformly distributed in the circumferential time t _0.

  Thus, by providing the non-accelerated circulation time, the difference in the circulation time caused by the variation in energy of the incident ion beam becomes large, so that the variation in the current value of the ion beam can be flattened.

FIG. 4 is a simulation result showing the distribution change of the current value of the ion beam when the ion beam is circulated without being accelerated by the synchrotron 16.
4A shows the time change of the current value of the incident ion beam, and FIG. 4B shows the time change of the current value when the non-accelerated circulation time is set to 0.5 m (s). (C) shows the time change of the current value when the non-accelerated lap time is set to 1 m (s).

Here, the incident beam of pulse width (FWHM) is ^5e -7 (s), and ^2.2e -6 (s) the circulation time of the ions having a nominal energy _{E 0.} The simulation is performed with the rated energy E ₀ as 4 MeV / u and the energy spread as ± 0.2% (assuming that the energy spread is uniform).

  The non-accelerated lap time T = 0.5 msec (after 220 laps), the current peak value is about 60% of the incident time (FIG. 4B). And it distributes substantially uniformly in the non-accelerated lap time T = 1 msec (after 440 laps) (FIG. 4C).

  FIG. 5 is a flowchart showing an ion beam acceleration control method according to the present embodiment (see FIG. 1 as appropriate).

  The incident beam control unit 25 starts laser irradiation with the laser ion source 11 and outputs a short pulse ion beam from the linear accelerator 12 (S10). The output ion beam is incident on the synchrotron 16 via the incident beam transport system 15 (S11).

  The synchrotron control unit 27 circulates the ion beam without accelerating without activating the high-frequency accelerating cavity 22 until the non-accelerated circulation time elapses from the timing of ion beam incidence (S12, S13: NO).

  After the non-acceleration lap time has elapsed, the high-frequency acceleration cavity 22 is activated (excited) to accelerate the ion beam (S13: YES, S14).

  The synchrotron control unit 27 maintains the acceleration state with the synchrotron 16 and executes extraction of the ion beam from the outgoing beam transport system 23 when the ion beam reaches the set energy (S15).

  As described above, when the ion beam is circulated without being accelerated by the synchrotron 16, the lap time difference caused by the energy variation of the incident ion beam is increased, and the variation in the current value of the ion beam is flattened. Thereby, when the ion beam is accelerated, it becomes possible to suppress a difference in current value for each bunch.

  Furthermore, as shown in FIG. 3, by setting the non-accelerated lap time so that the lap time difference caused by the energy variation of the incident ion beam is equal to or greater than the lap time of ions having the rated energy in the ion beam, The ion beam is uniformly distributed within the circulation time. Thereby, when the ion beam is accelerated, it is possible to eliminate the bias of the ion current value for each bunch.

  FIG. 6 is a configuration diagram illustrating an example of the particle beam therapy system 32 to which the ion accelerator 10 according to the present embodiment is applied.

  The particle beam therapy system 32 includes an ion accelerator 10, an outgoing beam transport system 23, and an irradiation device 29.

  The ion beam accelerated by the ion accelerator 10 is taken out via the outgoing beam transport system 23 and transported to the irradiation device 29. Then, the patient 30 lying on the treatment table 31 is inserted into the irradiation device 29, and the affected part of the patient 30 is irradiated with an ion beam to be treated.

  By applying the ion accelerator 10 according to the present embodiment, it is possible to realize the particle beam therapy system 32 in which the number of constituent devices can be reduced and the ion beam can be easily controlled.

  According to the ion accelerator described above, the ion beam can be circulated without accelerating the ion beam incident on the synchrotron for a predetermined time, and can be generated when the ion beam is circulated and accelerated. Variations in the current value for each bunch can be suppressed.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 10 ... Ion accelerator, 11 ... Laser ion source, 12 ... Linear accelerator, 13 ... Drift tube linear accelerator, 14 ... Deflection electromagnet, 15 ... Incident beam transport system, 16 ... Synchrotron, 17 ... Deflection electromagnet, 18 ... Quadrupole electromagnet , 19 ... 6-pole electromagnet, 20 ... Electrostatic septum for incidence, 21 ... Kicker electromagnet for incidence, 22 ... High-frequency acceleration cavity, 23 ... Emission beam transport system, 24 ... Control device, 25 ... Incident beam controller, 26 ... Timing Control part, 27 ... Synchrotron control part, 28 ... Non-acceleration lap time setting part, 29 ... Irradiation device, 30 ... Patient, 31 ... Treatment table, 32 ... Particle beam therapy apparatus.

Claims (4)

A laser ion source for generating plasma using a laser;
A linear accelerator that outputs an ion beam accelerated by extracting ions from the plasma;
A bending electromagnet for circulating the ion beam on a circular orbit and a high-frequency acceleration cavity for accelerating the ion beam orbiting the circular orbit are provided. With Tron,
A non-accelerated orbiting time setting unit that sets a time for orbiting the circular orbit of the synchrotron without accelerating the ion beam as an unaccelerated orbiting time;
A synchrotron control unit that activates the high-frequency acceleration cavity after the non-accelerated circulation time has elapsed after the ion beam is incident on the synchrotron, and accelerates the ion beam in a circular manner; and
The non-acceleration lap time is the time for the ion beam to circulate without accelerating until the lap time difference caused by variations in the energy of the incident ion beam is equal to or greater than the lap time of ions having the rated energy in the ion beam. ion accelerator characterized in that it. 2. The ion accelerator according to claim 1, wherein the ion beam is incident on the synchrotron by single-turn incidence in which the pulsed ion beam is incident in a single shot. A deflecting electromagnet for circulating an ion beam on a circular orbit and a high-frequency acceleration cavity for accelerating the ion beam circulating on the circular orbit are provided. ,
Generating a plasma using a laser;
Outputting the ion beam accelerated by extracting ions from the plasma;
Setting the time to circulate on the circular orbit of the synchrotron without accelerating the ion beam as a non-accelerated lap time;
After the ion beam is incident on the synchrotron, the steps of the activates the high-frequency accelerating cavity wherein is circulating accelerating the ion beam after the no-acceleration circulation time has passed, the Nde including,
The non-acceleration lap time is the time for the ion beam to circulate without accelerating until the lap time difference caused by variations in the energy of the incident ion beam is equal to or greater than the lap time of ions having the rated energy in the ion beam. ion acceleration control wherein the at. The ion accelerator according to claim 1 or 2 ,
An outgoing beam transport system that takes out and transports an ion beam accelerated by the ion accelerator;
A particle beam therapy system comprising: an irradiation device that irradiates an affected area of a patient with the ion beam guided through the outgoing beam transport system.

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